Assessment of exposure to drug use and psychosocial stress is complicated by the fact that each is often transient and difficult to recall accurately. Assessment of their causal connections with one another, and of their genetic and environmental determinants, is complicated by the complexity of the causal connections and by the elusive nature of what constitutes the environment. In this project, we are assessing drug use and psychosocial stress in near-real time through Ecological Momentary Assessment (EMA), in which participants use handheld electronic diaries to record events as they occur and to report recent or ongoing events in response to randomly timed prompts throughout the day. We are also maintaining real-time records of where the reported events occur by having participants carry Global Positioning System (GPS) loggers to track their whereabouts with a spatial resolution of several meters. We use these data collectively in a method we are calling Geographical Momentary Assessment (GMA). Our goal with GMA has little to do with knowing the specific Baltimore locations where drug-related behaviors occur, and everything to do with gaining generalizable knowledge about how activity spaces (the spaces in which daily activities occur) are associated with such behaviors and their precipitants. To that end, we score neighborhood environments in terms of objective statistical data andmore innovativelyin terms of objective ratings by trained observers. For many addiction researchers, such as behavioral geneticists and pharmacological clinical trialists, these environmental measures will constitute noise to be controlled for, so the benefit of GMA to them will be to help isolate the biological measures of interest. For addiction researchers with a social-science focus, the environmental measures will be signal rather than noise, so the benefit of GMA will be to make a case for environmental interventions and to provide a rigorous way of assessing the interventions implementation and effectiveness. To increase the objectivity of our field methods, we have added ambulatory monitoring of physiological functions such as respiration, heart-rate variability, and galvanic skin response. Our goals for these measures include the development of algorithms that can automatically detect behavioral events (such as episodes of drug use or stress) without requiring self-report. To help validate our field methods, we are collecting thrice-weekly urine specimens from all our participants and assessing their trait stress reactivity through standardized laboratory procedures. Our six publications from this set of projects have all used data from the first such project we completed, which was an EMA study that did not incorporate GPS. In the most recent of those publications, we showed that our cocaine- and heroin-abusing outpatients reported less stress and greater happiness (and less drug craving) at the workplace than in any other setting. This was a surprising result, precisely opposite to what has been reliably found in the general population. We do not facilely draw causal conclusions from this non-experimental finding, but we do conclude that experimental interventions are warranted. We continue to analyze data from our first EMA study, but our focus is on completing a larger study that incorporates GPS along with additional EMA measures of stress.